I replaced about 200 toilets in a tower once and One of them cause a significant amount of splash out of the bowl.. So the manufacture sent an engineer out and we went around to each of them and performed multiple flushes with a clear sheet of plexiglas to observe the splash pattern. There was a certain amount of splash that was deemed acceptable or not. Out of the 200, 15 were unacceptable and were scheduled for replacement. But instead, the engineer got out a set of small files and ground down the porcelain around the areas causing the splash and we didn't replace a single one.. we finished early and went and had beers instead.
Saran wrap is a good substitute if you don't have plexiglas, just remember to remove it before anyone else uses the toilet.